Climate protection: 80-meter high-rise without any concrete

Wooden skyscrapers are the trend for more sustainability and climate protection. At the top are European buildings with the 85.4 meter high 18-storey Mjøstårnet in Brumunddal, Norway and the Hoho Wien with 24 storeys (84 meters) in the seaside town of Aspern. After many years of planning, the Pi project in Zug, Switzerland, will join this group of pioneering buildings from 2022. The special thing about it: the 80-meter-high wooden high-rise with 27 floors, unlike previous buildings, does not have a stabilizing core made of concrete.

In the Pi project, engineers and architects working with Urban Assets Zug AG rely on a previously unique structural analysis. For the load-bearing structure of the wooden high-rise, they use a tube-in-tube system that has previously been used for high-rise buildings made of steel and concrete with a height of over 300 meters. No inner concrete core is supposed to stabilize the building against wind loads, but rather interlocking tubular structures that run all around over all floors. Horizontal and vertical loads are absorbed by a frame structure made of beech wood and special wood composite flat ceilings, the core elements of the construction.

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The stability of the beech veneer plywood, which is up to 40 centimeters wide, was checked in extensive load tests at the Institute for Structural Analysis and Design at ETH Zurich. This construction also leads to a unusual structure of the entire building. The size of the wooden high-rise increases in four steps with increasing height – in stark contrast to classic, slim-line high-rise buildings.

This approach saves tens of thousands of tons of carbon dioxide compared to reinforced concrete high-rise buildings. With a view to the hybrid wooden high-rises in Vienna and Brumunddal, the carbon footprint of the Pi project, which is around a fifth lighter, is expected to be 1,700 tons of carbon dioxide lower. This adds up to 3333 tons of CO2that remain stored in wood as a building material. In addition, with photovoltaic modules in the facade, the building itself becomes an energy producer and covers at least a small part of the needs of the planned apartments, studios and workshops.

Today, the planning and construction of wooden high-rises are more complex and expensive than classic reinforced concrete structures. But in order to be able to achieve ambitious climate targets in the building sector too, alternatives to steel and concrete are being sought. With an annual production of more than 4,000 million tons, the cement industry plays an important role in global warming. With an estimated six to seven percent, it emits more than twice as much CO2 free like all air traffic (2.8 percent).


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